British horticulturist Monty Don has highlighted the importance of delaying grass cutting until after June 21. Although it might be tempting to trim your gardens in time for summer BBQs, the 69-year-old emphasised that it’s crucial to let the grass grow and thrive for as long as possible.
“Nothing should be cut at all until after the longest day on June 21,” Monty wrote in a blog last year. “This gives the foliage of the bulbs time to die back and feed next year’s bulb and subsequent flowering.
“The grass can then be cut if it has been hot and dry although sometimes I leave this as late as mid-August.” Even though Monty’s advice was penned in 2024, the longest day of 2025, typically referred to as the summer solstice, likewise occured on June 21 (Saturday).
In the UK, grass growth is usually at its peak in April and May, driven by rising temperatures and rainfall. Prolonging this growth period as much as possible could enhance its health in the approaching spring.
Monty typically plants spring bulbs and wildflowers alongside his grass, creating a beneficial habitat for insects and wildlife. He emphasised the importance of collecting grass clippings after mowing and placing them in a compost heap.
Leaving them on the ground could promote the growth of ‘lusher coarser grasses,’ but it would disadvantage the flowers. Monty’s reflections follow a 2019 study by Plantlife that revealed most gardeners mow their grass biweekly, according to the Express.
The Royal Horticultural Society (RHS) has similarly suggested that leaving grass uncut until August fosters a greater diversity of plants, and it even supports the ‘No Mow May’ initiative to promote this approach.
However, it has also pointed out that mowing practices should be evaluated on an individual basis. For example, if weather conditions are unpredictable or grass growth is slower than expected, it might be prudent to reassess mowing decisions.
The RHS has advised: “In summer: with a conventional lawn, mow once a week on average, dropping to once a fortnight, or longer, during periods of drought.
“Flower-rich lawns can be mown every four to six weeks. Long-grassed lawns are best cut once or twice over the summer, usually not before June.”
When mowing long grass for the first time in a year, setting the mower to the highest blade setting is crucial to prevent clogging from grass clippings.
If the grass is exceptionally tall, the RHS suggests strimming it first to lower its height. Remember to gather any clippings before making the final cut with the mower.
It also added: “While you can restart mowing in June, it’s even better to leave the grass uncut until August to preserve the newly created habitat and encourage a greater diversity of plants.”